CROSS REFERENCE TO RELATED APPLICATIONS
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to a profile measuring device such as a three-dimensional
measuring instrument executing displacement measurement using a contact, a method
for profile measuring, and a program for profile measuring, the latter being not claimed.
Description of the Related Art
[0003] Generally, a contact in a contact measurement system using a contact type probe (contact)
is assumed to be a sphere, and a position of a center of the sphere is assigned as
a measurement point. The measurement point in this case differs from a position where
the contact makes contact with an object-to-be-measured. This causes an error with
respect to an actual profile of the object-to-be-measured.
[0004] Consequently, Japanese Unexamined Patent Application Publication No.
2001-280947 (patent document 1) describes a configuration in which an error of a profile of the
contact from a sphere is obtained in advance and correction is made by adding the
error component to the radius thereof as well. Note that in patent document 1 the
measurement point is derived as it is located on a direction normal to a locus of
the center of the contact.
[0005] Furthermore, Japanese Unexamined Patent Application Publication No.
08-43078 (patent document 2) describes a configuration in which a measurement point derivation
vector for each normal direction to a surface of the contact is obtained in advance,
and the measurement point is derived referring to the measurement point derivation
vector. In this patent document 2, a measurement point is determined from a vector
which is referred to using a normal direction to the locus of the center of the contact
as an index.
[0006] Moreover, Japanese Unexamined Patent Application Publication No.
2007-212359 (patent document 3) describes a configuration in which a contact model is allocated
along a locus of a certain position of the contact and the measurement point is derived
on the basis of the contact model and the measurement point derivation vector.
[0007] However, the configuration disclosed in patent document 1 has a problem that the
profile of the contact is limited to a sphere-like profile, and that measurement accuracy
becomes low in a case where the profile of the contact differs greatly from the sphere.
[0008] Furthermore, the configurations disclosed in patent documents 2 and 3 have a problem
that disturbances in the locus of the center of the contact arising from measurement
error make it difficult to derive the measurement point.
[0009] US2007/0208533 describes a configuration in which a geometric shape filter is used.
SUMMARY OF THE INVENTION
[0010] In accordance with an aspect of the present invention, a profile measuring device
that causes a contact to follow a surface of an object-to-be-measured and measures
a profile of the surface of said object-to-be-measured is provided. This device comprises:
an acquiring section that acquires, as pseudo-measurement points, positional coordinates
of a basing point of said contact when said contact is in contact with said object-to-be-measured
at a plurality of places, or acquires profile data related to the profile of the surface
of said object-to-be-measured; a contact model allocating section that allocates a
contact model by matching a basing point of said contact model to one of said pseudo-measurement
points or said profile data, and matching an orientation of said contact and said
contact model at a time of measuring, said contact model specifying a surface profile
of said contact and having a predetermined definition range; a measurement point acquiring
section that acquires, as measurement points, positions of the surface of said object-to-be-measured
based on said contact model as well as said pseudo-measurement points or said profile
data; and a measurement point deleting section that deletes a measurement point obtained
by said measurement point acquiring section based on a relationship between said definition
range and said measurement points.
[0011] In accordance with the aspect of the present invention, a method of measuring a profile
of a surface of an object-to-be-measured by causing a contact to follow the surface
of the object-to-be-measured is provided. The method comprises: acquiring, as pseudo-measurement
points, positional coordinates of a basing point of said contact when said contact
is in contact with said object-to-be-measured at a plurality of places or acquiring
profile data related to the profile of the surface of said object-to-be-measured;
allocating a contact model by matching a basing point of said contact model to one
of said pseudo-measurement points or said profile data, and matching an orientation
of said contact and said contact model at a time of measuring, said contact model
specifying a surface profile of said contact and having a predetermined definition
range; acquiring, as measurement points, positions of the surface of said object-to-be-measured
based on said contact model as well as said pseudo-measurement points or profile data;
and deleting a measurement point obtained by said measurement point acquiring section
based on a relationship between said definition range and said measurement points.
[0012] A program for profile measuring configured to cause a computer to execute the corresponding
method is provided (not claimed).
BRIEF DESCRIPTION OF THE DRAWINGS
[0013]
Fig. 1 is a schematic configuration view of a profile measuring device in accordance
with a first embodiment of the present invention.
Fig. 2 is a functional block diagram of the profile measuring device in accordance
with the first embodiment of the present invention.
Fig. 3 is a flowchart describing an operation of the profile measuring device in accordance
with the first embodiment of the present invention.
Fig. 4 is a view describing an operation to acquire a pseudo-measurement point Ak in the profile measuring device in accordance with the first embodiment of the present
invention.
Fig. 5 is a view describing an operation to generate a guide line Bk in the profile measuring device in accordance with the first embodiment of the present
invention.
Fig. 6 is a view describing an operation to allocate a contact model C in the profile
measuring device in accordance with the first embodiment of the present invention.
Fig. 7 is a view describing an operation to acquire an intersection point Pk and a measurement point Mk in the profile measuring device in accordance with the first embodiment of the present
invention.
Fig. 8 is an enlarged view of the region AR in Fig. 7.
Fig. 9 is a view describing the operation to acquire the measurement point Mk in the
profile measuring device in accordance with the first embodiment of the present invention.
Fig. 10 is a view describing an effect of the profile measuring device in accordance
with the first embodiment of the present invention.
Fig. 11 is a schematic view describing the contact model C.
Fig. 12 is a descriptive view showing a relationship between a measurement range of
a corrected measurement and a definition range DA of the contact model C.
Fig. 13 is a descriptive view showing the relationship between the measurement range
of the corrected measurement and the definition range DA of the contact model C.
Fig. 14 is a conceptual view showing a difference between a calculated measurement
point sequence Mk and a work surface in a case that an object to be measured having
a semispherical profile is measured.
Fig. 15 is a conceptual view describing a procedure to delete the measurement point
Mk from the measurement point sequence (step S16).
Fig. 16 is a conceptual view describing the procedure to delete the measurement point
Mk from the measurement point sequence (step S16).
Fig. 17 is a conceptual view describing the procedure to delete the measurement point
Mk from the measurement point sequence (step S16).
Fig. 18 is a conceptual view describing the procedure to delete the measurement point
Mk from the measurement point sequence (step S16).
Fig. 19 is a conceptual view describing the procedure to delete the measurement point
Mk from the measurement point sequence (step S16).
Fig. 20 is a functional block diagram of a profile measuring device in accordance
with a second embodiment of the present invention.
Fig. 21 is a flowchart describing an operation of the profile measuring device in
accordance with the second embodiment of the present invention.
Fig. 22 is a conceptual view describing the operation of the profile measuring device
in accordance with the second embodiment.
Fig. 23 is a conceptual view describing the operation of the profile measuring device
in accordance with the second embodiment.
Fig. 24 shows a variant example of an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0014] A profile measuring device in accordance with an embodiment of the present invention
is now described with reference to the drawings.
First Embodiment
Configuration of the profile measuring device in accordance with a first embodiment
[0015] Fig. 1 is a perspective view showing a schematic configuration of the profile measuring
device in accordance with the first embodiment of the present invention. This profile
measuring device is configured from a three-dimensional measuring instrument 1, and
a computer 2 that drives and controls this measuring instrument 1 to download a required
measurement value, and executes an arithmetic processing required for a profile processing.
[0016] The three-dimensional measuring instrument 1 is configured as shown in Fig. 1, for
example. It is equipped with a vibration-removing platform 10. A surface table 11
is positioned on the vibration-removing platform 10 such that its upper surface as
a base surface coincides with a horizontal plane.
[0017] A beam 13 extending in an X axis direction is supported by upper ends of beam supports
12a and 12b. These beam supports 12a and 12b are vertically extended from both end
sides of this surface table 11.
[0018] The beam support 12a has a lower end thereof driven in a Y axis direction by a Y
axis drive mechanism 14. Furthermore, the beam support 12b has a lower end thereof
supported by an air bearing to be movable in the Y axis direction on the surface table
11. The beam 13 supports a column 15 extending in a vertical direction (Z axis direction),
The column 15 is driven in the X axis direction along the beam 13. The column 15 is
provided with a spindle 16 such that the spindle 16 is driven in a Z axis direction
along the column 15. Attached to a lower end of the spindle 16 is a probe 17 of a
contact type. Moreover, formed at a leading end of the probe 17 is a contact 17a of
a certain profile, for example, of an elliptically spherical profile. When this contact
17a makes contact with a surface 31a of an object-to-be-measured 31 positioned on
the surface table 11, a touch signal is outputted, and an XYZ coordinate value of
a reference position of the contact 17a at that time is downloaded to the computer
2.
[0019] The computer 2 comprises a computer main unit 21, a keyboard 22, a mouse 23, a CRT
24 and a printer 25.
[0020] Fig. 2 is a functional block diagram of this profile measuring device.
[0021] The three-dimensional measuring instrument 1 includes therein an XYZ motor 18 and
an XYZ encoder 19. The YZ axis motor 18 serves for driving the probe 17 in XYZ axis
directions. The XYZ encoder 19 outputs a movement pulse for each axis direction based
on movement in the XYZ axis directions. Moreover, when there is a contact of the contact
17a with the surface 31a of the object-to-be-measured 31, the XYZ encoder 19 acquires
positional information of a basing point of the contact 17a (for example, a center
of gravity of the contact 17a). The positional information obtained is stored in a
storage section 210a.
[0022] The computer main unit 21 of the computer 2 is configured mainly from the storage
section 210a and a control section 210b. The storage section 210a comprises, for example,
an HDD, semiconductor memory, or the like. The control section 210b is realized by
a profile measuring program that calculates a measurement point based on information
stored in the storage section 210a, or drives the three-dimensional measuring instrument
1, and a CPU or the like for executing the profile measuring program.
[0023] The storage section 210a stores information of a position and orientation of the
contact 17a at a time of measuring, information of a profile of the contact used in
measuring, information calculated by the control section 210b to be described hereafter,
and so on.
[0024] The control section 210b is provided with an operation command section 211, a pseudo-measurement
point acquiring section 212, a guide line generating section 213, a contact model
allocating section 214, an intersection point acquiring section 215, a measurement
point acquiring section 216, a measurement point deleting section 217, and a surface
profile determining section 218.
[0025] The operation command section 211 causes the contact 17a to follow the surface 31a
of the object-to-be-measured 31 through the XYZ axis motor 18 based on an input value
from the keyboard 22 and mouse 23.
[0026] The pseudo-measurement point acquiring section 212 acquires, as a pseudo-measurement
point, positional information of a basing point (for example, a position of the center
of gravity) of the contact 17a at a time of a contact of the contact 17a with the
object-to-be-measured 31 at a plurality of places.
[0027] The guide line generating section 213 generates a guide line directed approximately
in a direction from the pseudo-measurement point towards a surface of the object-to-be-measured.
[0028] The contact model allocating section 214 allocates a contact model by matching to
the pseudo-measurement point a basing point of the contact model, and matching an
orientation of the contact and the contact model at the time of measuring, the contact
model specifying a surface profile of the contact 17a.
[0029] The intersection point acquiring section 215 acquires an intersection point at which
each guide line and a surface of each allocated contact model intersect.
[0030] The measurement point acquiring section 216 acquires, as a measurement point, the
intersection point most distant from the pseudo-measurement point among the intersection
points with each guide line.
[0031] The measurement point deleting section 217 deletes a portion of the measurement points
acquired by the measurement point acquiring section 216 in accordance with a predetermined
protocol.
[0032] The surface profile determining section 218 determines a profile of the object-to-be-measured
based on each measurement point acquired by the measurement point acquiring section
216 and selected by the measurement point deleting section 217. Note that this information
obtained by the control section 210b is stored in the storage section 210a.
Operation of the profile measuring device in accordance with the first embodiment
[0033] A measurement point acquiring method using the profile measuring device in accordance
with the first embodiment is now described in line with the flowchart shown in Fig.
3, and making appropriate reference to Figs. 4-9. Note that, for simplification, Figs.
4 to 9 are shown two-dimensionally as cross-sectional views of the object-to-be-measured.
[0034] First, the operation command section 211 causes the contact 17a to be in contact
with the surface 31a of the object-to-be-measured 31 based on an operation of the
keyboard 22 and the mouse 23 by a user, thereby scanning the probe 17 linearly in
a predetermined direction, as shown in Fig, 4. Along with this, the pseudo-measurement
point acquiring section 212 detects positions where the contact 17a made contact with
the surface 31a of the object-to-be-measured 31 to acquire a pseudo-measurement point
A
k (k = 1∼n) (step S11). Note that measurement in this process of step S11 may be either
point measurement or scanning measurement.
[0035] Next, the guide line generating section 213 generates guide lines B
k (k = 1∼n) directed approximately in a direction from the pseudo-measurement points
A
k towards the surface 31a of the object-to-be-measured 31 (step S12), as shown in Fig.
5. For example, each of the guide lines B
k is generated in a range of ±45 °from a normal to a locus of the pseudo-measurement
points A
k. Note that Fig. 5 shows an example in which the guide lines B
k are generated to be parallel to one another; however, the guide lines B
k need not necessarily be parallel to one another.
[0036] Subsequently, the contact model allocating section 214 executes allocation of a contact
model C, by matching to the respective pseudo-measurement points A
k a basing point D of a contact model C, the basing point D being a predetermined position
of the contact model C, and matching an orientation of the contact 17a at the time
of measuring and an orientation of the contact model C (step S13), as shown in Fig.
6. The contact model C allocated by matching the basing point D to the pseudo-measurement
point A
k is hereafter referred to as contact model C
k. Note that, although Fig. 6 describes only concerning one pseudo-measurement point
A
k, the contact model allocating section 214 executes this processing on all the pseudo-measurement
points A
k (k = 1∼n).
[0037] Next, the intersection point acquiring section 215 acquires an intersection points
P
k,j (k = 1∼n, j = 1∼m) of a surface Ca
k (k = 1∼n) of the contact model C
k (k = 1∼n) and the guide lines B
k (k = 1∼n) (step S14). Then, the measurement point acquiring section 216 acquires,
as a measurement point M
k, the intersection point P
k,j most distant from the pseudo-measurement point A
k among the intersection points P
k,j with each guide lines B
k (step S15).
[0038] Here, a specific example of step S14 and step S15 is described referring to Fig.
7 and Fig. 8. Fig. 7 is a view showing the surfaces Ca
k-5∼Ca
k+5 of the contact models C
k-5∼C
k+5 allocated to the pseudo-measurement points A
k-5∼A
k+5, centered around one pseudo-measurement point A
k, Furthermore, Fig. 8 is an enlarged view of the region AR in Fig. 7.
[0039] In step S14 of the example shown in Fig. 7 and Fig. 8, 10 intersection,points P
k,1∼P
k,10 with the guide line By are acquired, Here, the notation "P
x (B
x, Ca
x)" is adopted to describe the fact that the intersection point P
x is the intersection point of the guide line B
x and the surface Ca
x. If such a notation is adhered to, the above-described intersection points P
k,1∼P
k,10 can be expressed as "P
k,1 (B
k, Ca
k+5 (or (Ca
k-5))", "P
k,2 (B
k, Ca
k+4)", "P
k,3 (B
k, Ca
k-4)", "P
k,4 (B
k, Ca
k+3)", "P
k,5 (B
k, Ca
k-3)", "P
k,6 (B
k, Ca
k+2)", "P
k,7 (B
k, Ca
k-2)", "P
k,8 (B
k, Ca
k+1)", "P
k,9 (B
k, Ca
k-1)", "P
k,10 (B
k, Ca
k)".
[0040] Further, in step S15 of the example shown in Fig. 7 and Fig. 8, the intersection
point P
k,10 most distant from the pseudo-measurement point A
k among the intersection points P
k,1∼P
k,10 with each guide line B
k is acquired as the measurement point M
k. After undergoing a processing of the above-described steps S11∼S15, each measurement
point M
k (k = 1∼n) corresponding to each pseudo-measurement point A
k is acquired, as shown in Fig. 9.
[0041] As described above, the profile measuring device in accordance with the first embodiment
acquires the intersection point P
k,j of the contact model C
k allocated to the pseudo-measurement point A
k and the guide line B
k extending from the pseudo-measurement point A
k, and acquires as the measurement point M
k the intersection point P
k,j most distant from the pseudo-measurement point A
k.
[0042] Here, other configurations (comparative examples) differing from the present embodiment
may be considered as a method for acquiring the measurement point M
k. For example, in one of the other configurations, pseudo-measurement points A'
k (k = 1∼n) are first acquired, a surface (or line) fitted to the pseudo-measurement
points A'
k is estimated, and measurement point deriving vectors B'
k (k = 1∼n) are generated. The vector B'
k (k= 1∼n) are perpendicular lines extending from the pseudo-measurement points A'
k to that surface. Then, in the one of the other configurations, positions located
on the measurement point deriving vectors B'
k and separated from the pseudo-measurement points A'
k by a predetermined distance are acquired as the measurement points M'
k (k = 1∼n).
[0043] However, in the above-described configuration, there arises the following problem.
Specifically, as shown in Fig. 10A, when a surface 32a of an object-to-be-measured
32 is measured along a predetermined direction, and some of the acquired pseudo-measurement
points, for example, pseudo-measurement points A'
k+1, A'
k+2 may be greatly deviated, due to measurement error, compared to the other pseudo-measurement
points.
[0044] In this case, the measurement points M'
k (k = 1∼n) differ from an actual profile of the surface 32a of the object-to-be-measured
32, as shown in Fig. 10B. That is to say, as shown by the measurement points M'
k∼M'
k+3 in Fig. 10B, although measurement points are obtained by measuring the surface 32a
of the object-to-be-measured 32 along a predetermined direction, a locus O' linking
these measuring points M'
k forms a loop.
[0045] On the other hand, according to the profile measuring device in accordance with the
first embodiment of the present invention, even when the surface 32a of the object-to-be-measured
32 as shown in Fig. 10A is measured along a predetermined direction, and, as shown
in Fig. 10B, the pseudo-measurement points A'
k+1, A'
k+2 are greatly deviated compared to the other pseudo-measurement points due to measurement
error, the locus O linking the measurement points M
k does not form a loop, and the measurement points M
k are close to the actual profile of the surface 32a of the object-to-be-measured 32.
[0046] That is to say, the profile measuring device in accordance with the first embodiment
may acquire accurate measurement points, even if the profile of its contact is not
an ideal sphere.
[0047] Note that, in the first embodiment, when distances between the pseudo-measurement
points acquired by the pseudo-measurement point acquiring section 212 are large, interpolation
processing may be executed in the pseudo-measurement point acquiring section 212 to
interpolate the pseudo-measurement points, for example. It is also possible to provide
an interpolating section independently from the pseudo-measurement point acquiring
section 212.
[0048] Description is continued returning once again to Fig. 3. When a plurality of the
measuring points M
k configuring a measurement point sequence are obtained as described above, a number
of measurement points included in the plurality of measurement points M
k are deleted from the measurement point sequence, if it is supposed that these measuring
points include large errors (step S16).
[0049] In the present embodiment, the contact model C has a definition range DA defined
by an angle ±θd, and a portion of the measurement points M
k are deleted from the measurement point sequence based on this definition range DA,
as shown in Fig. 11. A process for deleting the measurement points M
k is now described in detail referring to the drawings.
[0050] The definition range DA of the contact model C is defined as a fan-shaped area symmetrically
widening from a vertical line N dropped from the basing point D (angle θd to the right
of the vertical line, angle -θd to the left of the vertical line), for example, as
shown in Fig. 11. This definition range DA is calculated from an outline of a pseudo-measurement
point sequence obtained by measuring a reference measurement object having a known
profile. The broader a measurement range of this calibration measurement, the broader
the definition range DA (the larger the angle θd); the narrower the measurement range
of the calibration measurement, the narrower the definition range DA (the smaller
the angle θd).
[0051] In a case that the definition range DA is broad, almost no error occurs in a calculation
of the measurement points M
k based on the calculated pseudo-measurement points A
k, as shown in Fig. 12. However, in a case that the definition range DA is narrow,
the greater an inclination of a measurement surface of the object-to-be-measured becomes,
the more the calculated measurement point M
k departs from an actual surface of the object-to-be-measured (work surface) resulting
in a large error, as shown in Fig. 13. This is because an error in the calculation
occurs due to the fact that the object-to-be-measured and the contact are actually
making contact outside the definition range DA. Fig. 14 shows a difference between
the calculated measurement point M
k and the work surface in a case of measuring an object-to-be-measured that has a semispherical
profile. The greater an inclination of the work surface, the larger the difference
between the work surface and the measurement point sequence becomes; however, it is
difficult to distinguish whether this is based on a profile of the work surface, or
based on a measurement error.
[0052] Consequently, in the present embodiment, only the measurement points M
k obtained when the contact 17a and the object-to-be-measured make contact inside the
definition range DA of the contact model C are left (without being deleted) in the
measurement point sequence, whereas the measurement points Mk obtained when the contact
17a and the object-to-be-measured make contact outside the definition range DA are
deleted from the measurement point sequence. Specifically, in a case that an angle
θm from the vertical line N of a directional vector V
k directed from the basing point D to the calculated measurement point M
k is smaller than θd as shown in Fig. 15, the measurement point so obtained is determined
on an inside and not an outside of the definition range DA as shown in Fig. 16. An
error between the measurement point M
k obtained in such a case and an actual contact point Pc is considered to be small,
and the measurement point M
k is thus not deleted from the measurement point sequence but allowed to remain.
[0053] In contrast, in a case that the angle θm from the vertical line N of the directional
vector V
k is found to be equal to ±θd (θm = ±θd) as shown in Fig. 17, the actual contact point
Pc is supposed to be outside of the definition range DA, and the error between the
measurement point M
k obtained and the actual contact point Pc is considered to be large. Consequently,
such a measurement point M
k set in the outside (edge) of the definition range DA is deleted from measurement
point sequence.
[0054] For example, as shown in Fig. 19, in the contact models C set at positions in which
the inclination of the work surface is large (numbers 1, 2, 10, and 11), the measurement
points M
k are obtained as θm = ±θd, and these measurement points M
k are thus deleted from the measurement point sequence (shown by a cross mark in Fig.
19),
[0055] In accordance with the above, a process for acquiring the measurement point sequence
is completed, and the surface profile determining section 218 executes a determination
of the surface profile of the object-to-be-measured based on the measurement point
sequence obtained through the above steps.
[0056] Note that, although in the above description θm = θ d is set as a condition for deleting
the measurement point M
k, this is limited to a case of the configuration specifically described in the above
embodiment, and the present invention is obviously not limited to this.
Second Embodiment
[0057] A second embodiment of the present invention is now described in detail with reference
to the drawings. An external appearance of the profile measuring device is substantially
identical to that of the first embodiment (Fig. 1), and a description is therefore
omitted. Fig. 20 is a functional block diagram of the profile measuring device of
the present embodiment. Fig. 21 is a flowchart showing steps of executing the profile
measuring method in the present embodiment, and Figs. 22 and 23 are conceptual views
describing the profile measuring method in accordance with the present embodiment.
Note that identical symbols are assigned to parts that are identical to those in the
first embodiment, and repetitive descriptions are hereafter omitted.
[0058] In the first embodiment, the measurement points M
k are obtained by causing the contact 17a to actually move along the surface of the
object-to-be-measured and obtaining the pseudo-measurement points A
k in the pseudo-measurement point acquiring section 212, and then allocating the contact
models C such that the basing point D is matched to these pseudo-measurement points
A
k, In contrast to this, in the present embodiment, instead of actually measuring the
object-to-be-measured and obtaining the pseudo-measurement points in the pseudo-measurement
point acquiring section 212, a profile data acquiring section 219 that acquires profile
data (CAD data, and so on) of the object-to-be-measured is provided as shown in Fig.
20, and the profile data of the object-to-be-measured is acquired from an external
CAD system (not shown) for example as shown in Fig. 21 (step S11').
[0059] Then, the guide lines Bk are generated similarly to the first embodiment in accordance
with this profile data (step S12'), and the contact models C are allocated such that
the basing point D is matched to the profile data (step S13'). Subsequently, acquisition
of the intersection points P
k,j is executed in a substantially identical manner to the first embodiment (step S14').
Next, a procedure for acquisition of the measuring points M
k is executed (step S15'). The measurement points M
k here are not ones obtained by actually measuring the object-to-be-measured but are
measurement points resulting from simulation. Furthermore, this step S15' differs
from the step S15 of the first embodiment in that the intersection point P
k,j most distant from the profile data is acquired as the measurement point M
k.
[0060] Next, a portion of the plurality of measuring points M
k thus obtained is deleted from the measuring point sequence according to identical
criteria to the first embodiment (step S16'). After execution of the procedure for
deleting the measurement points M
k, a measurable range in which measurement by the contact model C is possible is determined
based on the remaining measurement point sequence (step S17').
[0061] That is to say, this embodiment differs from the first embodiment in that the contact
models C are allocated along the profile data (CAD data, and so on), not along the
pseudo-measurement points A
k obtained by actually measuring the object-to-be-measured. A range of the measurement
points M
k left undeleted by this procedure is determined as the measurable range in which measurement
by the contact model C is possible (defined by a maximum inclination angle of the
work surface).
[0062] As shown in Fig. 22, when a surface of arc-shaped object-to-be-measured having a
center point C is measured, measurement points M
k obtained at positions of numbers 3-6 remain without deletion, whereas measurement
points M
k obtained at positions of numbers 1, 2, 7, and 8 are deleted from the measurement
point sequence. Further, the measurable range that is measurable by the contact model
is determined based on borders between the remaining measurement points M
k and the deleted measurement points M
k. Here, the measurable range is determined, as shown in Fig. 23, by angles (θsl, θsr)
of the positions of numbers 2 and 7 that are deleted first as shown in Fig. 22. Determination
of the measurable range makes it possible to predict the actual measurable range in
subsequent measurement, and to avoid measurement in which the required measurement
accuracy is unobtainable. In addition, it is also possible to exclude from the measurement
point sequence the measurement points obtained outside the measurable range determined.
Furthermore, if there is dissatisfaction with the measurable range determined, the
measurement can also be discontinued and a separate contact substituted.
[Other Embodiments]
[0063] This concludes description of embodiments of the present invention, but it should
be noted that the present invention is not limited to the above-described embodiments,
and that various alterations, additions, substitutions, and so on, are possible within
a range not departing from the scope of the invention. For example, the three-dimensional
measuring instrument is taken as an example in the above-described embodiments but
the present invention is not limited to the three-dimensional measuring instrument
and can also be applied to a two-dimensional measuring instrument (for example, a
contour measurement contracer, and so on). Furthermore, in the above-described embodiments,
the contact model C of an elliptically spherical profile is set corresponding to the
contact 17a of an elliptically spherical profile but a spherical contact model corresponding
to a spherical contact may also be set in place of this,
[0064] Moreover, in the above-described embodiments, the definition range of the contact
model C is defined two-dimensionally but it may also be defined three-dimensionally
as shown in Fig. 24. That is to say, operations identical to those of the first and
second embodiments may also be executed in an intersection surface of a cross-sectional
surface containing the pseudo-measurement points A
k and the measurement points M
k, and this three-dimensional defined definition range DA.